Currently, a system (so-called an electric license plate system) is under development to transmit and receive various data between a wireless communication unit fixed on a vehicular license plate and outer apparatuses (roadside units) installed on sides of roads for a registration management of vehicles, a traffic control and the like (refer to JP-3236832-B, for example).
Commonly, the wireless communication unit used in this kind of system has a construction provided with units such as a wireless communication portion, a memory device portion and a power source portion. If these units are separately provided, an assembly of the product becomes complex and the units must be connected to each other by a harness and the like.
For example, if the system is constructed in such a manner that the wireless communication unit is operated by a power supply from an outer power source, a power supply cable must be provided to connect the outer power source to the wireless communication unit. This construction requires a wiring work which varies in accordance with types of vehicle, so that a workability of an installation of the wireless communication unit is spoiled and a versatility of the wireless communication unit is limited. Further, the construction that requires the wiring work may limit types of vehicle to which the wireless communication unit can be installed, so as to hinder a prevalence of the product.